Lubricants, such as lubricating oils and greases, are subject to oxidative deterioration at elevated temperatures or upon prolonged exposure to the elements. Such deterioration is evidenced, in many instances, by an increase in acidity and in viscosity, and when the deterioration is severe enough, it can cause metal parts to corrode. Additionally, severe oxidation leads to a loss of lubrication properties, and in especially severe cases this may cause complete breakdown of the device being lubricated. Many additives have been tried, however, many of them are only marginally effective except at high concentrations. Improved antioxidants are clearly needed.
Antioxidants or oxidation inhibitors are used to minimize the effects of oil deterioration that occur when hot oil is contacted with air. The degree and rate of oxidation will depend on temperature, air and oil flow rates and, of particular importance, on the presence of metals that may catalytically promote oxidation. Antioxidants generally function by prevention of chain peroxide reaction and/or metal catalyst deactivation. They prevent the formation of acid sludges, darkening of the oil and increases in viscosity due to the formation of polymeric materials.
Water (moisture) is another critical problem. In spite of even extraordinary precautionary efforts water is found as a film or in minute droplets in vessels containing various hydrocarbon distillates. This brings about ideal conditions for corrosion and damage of metal surfaces of the vessels and the materials contained therein. Also in the lubrication of internal combustion engines, for example, quantities of water are often present as a separate phase within the lubricating system. Another serious problem in respect to metallic surfaces in contact with adjacent metallic surfaces is the surface wear caused by the contact of such surfaces. One material capable of simultaneously effectively coping with such problems as these is highly desirous.
It has now been found that the use of a combination of Mannich type reaction products of ethoxylated alkylated phenol, and alkylated arylamine provide exceptional antioxidant activity. These remarkable benefits are to be expected for a variety of synthetic and mineral oil based lubricants.
To the best of our knowledge, this combination has not been previously used as additives in lubricating oils or greases. The additive products themselves and lubricant compositions thereof are both believed to be novel.
The use of arylamines as antioxidants in a variety of lubricant polymers and rubber applications is known. Also, the use of phenols are reported as having antioxidant properties, especially a low temperatures.
It has now been found that incorporative elements of phenol with alkylated arylamine provide exceptional synergistic antioxidant and high temperature stabilities. These elements also provide for good fluidity and enhanced oil solubility, far surpassing expectations.